Organized 31 December 1861 in the Regular Army at Washington, D.C., from new and existing companies of engineers as a provisional engineer battalion (constituted 28 July 1866 as the Battalion of Engineers)

Expanded 14 March-7 June 1901 to form the 1st Battalion of Engineers (hereafter separate lineage) and the 2d Battalion of Engineers

2d Battalion of Engineers expanded 1 July-1 August 1916 to form the 2d Regiment of Engineers

2d Regiment of Engineers expanded 21 May-20 June 1917 as follows:

Company C (see ANNEX), Company D (organized 24 August 1916 in Mexico), and part of Headquarters expanded 21 May 1917 to form the 5th Regiment of Engineers

(Companies A and B and part of Headquarters expanded 21 May 1917 to form the 2d Regiment of Engineers; Companies E and F and part of Headquarters expanded
4-20 June 1917 to form the 4th Regiment of Engineers--hereafter separate lineages)

5th Regiment of Engineers redesignated 29 August 1917 as the 5th Engineers

Assigned 6 December 1917 to the 7th Division

Inactivated 27 September 1921 at Camp Humphreys, Virginia

Relieved 1 February 1936 from assignment to the 7th Division and activated at Fort Belvoir, Virginia

Redesignated 1 August 1942 as the 5th Engineer Combat Regiment

Regiment broken up 27 December 1943 and its elements reorganized and redesignated as follows:

Headquarters and Headquarters and Service Company as Headquarters and Headquarters Company, 1128th Engineer Combat Group